Problem: $\text E = \left[\begin{array}{rr}1 & -1 \\ 1 & 2\end{array}\right]$ What is the determinant of $\text E$ ?
Answer: The determinant of a 2x2 matrix can be computed the following way: $ \left|\begin{array}{rr}a & b \\ c & d\end{array}\right| = (a \times d)-(b \times c) $ In this specific case, $ \left|\begin{array}{rr}1 & -1 \\ 1 & 2\end{array}\right| = (1 \cdot 2)-(-1 \cdot 1) $ $ = 3 $